The present invention relates to control of an etching process performed by dry etching apparatuses.
In conventional dry etching apparatuses, etching characteristics such as an etching rate and a uniformity are monitored by etching a dummy wafer. And if the etching characteristics are deviated from the standard values, the apparatus is cleaned.
FIG. 2 shows an example of a conventional ECR plasma etching apparatus. A wafer 13 is placed in a reaction chamber 1 made of quartz glass. Gases are introduced into the chamber 1 through a gas inlet 2, ionized to become a plasma by a combined action of a microwave which is generated by a magnetron 4 and introduced by a waveguide 5 and a magnetic field generated by solenoid coils 6. Resultant plasma particles are made incident on the wafer 13 by a radio-frequency voltage from a radio-frequency voltage supply 7, to etch the wafer 13. Reference numeral 3 denotes a gas outlet.
For example, using the apparatus of FIG. 2, a polycrystalline silicon layer formed on an SiO.sub.2 layer is etched in the following manner. A C.sub.2 Cl.sub.2 F.sub.4 gas and a SF.sub.6 gas are introduced into the chamber 1 by amounts of 63 and 7 SCCM, respectively, and a pressure is set at 10 mTorr. Powers of the microwave and radio-frequency voltage are set at 300 and 160 W, respectively. Plasma light emitted from the wafer 13 is provided to a detector 10 via a window 8 and an optical fiber 9. The detector 10 detects the plasma light to determine an end of the etching. Etching characteristics are monitored, at a certain frequency, by etching a dummy wafer to about a 70%-depth, and measuring a difference in level with a contact-type level-difference measuring device. With this procedure, the etching process can proceed at an etching rate of 3,000 .ANG. with a uniformity of .+-.5%, for example. If these etching characteristics are maintained, the etching process is performed satisfactorily without incurring such a case that the SiO.sub.2 layer is etched out at some portions completely, even if it is as thin as 200 .ANG..
However, if the etching uniformity exceeds the range of .+-.10% as the process goes on, there may arise such undesirable phenomena that the SiO.sub.2 layer is etched out at peripheral portions of the wafer 13 where the etching rate is high, and that the etching end cannot be determined because of a slowed decreasing rate of the plasma light intensity. Therefore, it is required to etch a dummy wafer at a higher frequency (e.g., one monitoring per 25 wafers) to monitor the etching characteristics.
Thus, in prior art apparatuses, the etching characteristics are measured using a dummy wafer, which requires extra time and labor.